1. Field of Invention
The invention relates to a fuel cooling system for a circulating fuel supply apparatus of an engine for a small watercraft, adapted to be supplied fuel into an injector from a fuel tank through a fuel supply pipe by a fuel supply pump, and to return excess fuel in the injector to a fuel tank through a fuel return pipe.
2. Description of Related Art
FIG. 6 shows a basic configuration of a circulating fuel supply apparatus. It is provided in an outboard engine, in which a fuel inlet port 14a of each injector 14 is connected to a fuel tank 6 via a fuel supply pipe 17 and a fuel pump 18, and an excess fuel return port 14b of each injector 14 is connected to the fuel tank 6 via a return pipe 19 and a vapor separator 50.
When such a circulating fuel supply apparatus, as shown in FIG. 6, is applied to the engine of a small watercraft, fuel temperature increases for the following reasons:
(1) When the fuel supply apparatus is operated in midsummer, the fuel tank itself is heated by the sunlight to cause the fuel temperature to increase in the interior of the fuel tank. Especially, a small watercraft that is used primarily in summer, has an engine compartment in the hill that has small dimensions as compared with those of an automobile or larger boat. The fuel tank is provided in a small space in the engine compartment with the engine, so that the temperature in the interior of the fuel tank 6 increases even more.
(2) In the circulating fuel supply apparatus, a part of fuel supplied by the fuel pump is used for the injection by the injector, and the remaining fuel in the injector is returned as an excess fuel to the fuel tank, so that the fuel, the temperature of which has been increased in the interior of the injector, returns with the increased temperature to the fuel tank. Therefore, the temperature in the interior of the fuel tank increases gradually as the operation of the circulating fuel supply apparatus continues.
In the case where an electromagnetic solenoid, for opening and closing a valve of the injector, is contained in the injector, the temperature of the injector itself increases, and this also constitutes one of the reasons for the rise in temperature of the fuel.
When fuel temperature increases excessively, variation occurs in the movements of the electromagnetic valve in the injector, and it is conceivable that proper fuel injection by the injector becomes difficult.
In order to prevent the fuel temperature rise in the circulating fuel supply apparatus in the prior art, as shown in FIG. 6, the vapor separator 50 is provided in the return pipe 19 of an outboard engine for cooling the fuel, whereby the vapor separator 50 works to remove a vaporized component of a return fuel and to cool the fuel. The vapor separator 50 can be provided only in the return pipe 19 which is low pressure due to the structure thereof. The related art is disclosed in Japanese KOUKAI Patent No. SHO60-104760.
In a circulating fuel supply apparatus in which the vapor separator 50 is provided in the return pipe 19, as shown in FIG. 6, the cooling effect for the fuel supplied to the injectors 14 is low, as will be described in the following:
(1) The quantity of the fuel returning from the return pipe 19 to the fuel tank 6 is small as compared with an absolute quantity of the fuel in the fuel tank 6. Therefore, even when the small quantity of the return fuel is cooled by the vapor separator 50, it can not sufficiently reduce the temperature of the fuel in the fuel tank. Consequently, it is difficult to sufficiently cool the fuel supplied to the injectors 14.
(2) A vaporized component is mixed in large quantities in the return fuel. Therefore, even when the fuel is cooled as a gas-liquid separation operation is carried out in the vapor separator 50, the cooling of the fuel is difficult as compared with that of the liquid component alone.
The invention has been made in view of the above circumstances, and provides a circulating fuel supply apparatus for a engine of a small watercraft, having a cooling device with a simple structure, and adapted to cool the fuel in the apparatus efficiently and supply the resultant fuel to an injector so as to repress, or minimize, vaporization of the fuel. Thus, cooling of the injector is done with a high reliability, and injection of the fuel by the injector is done properly.
The invention provides a circulating fuel supply apparatus for an engine of a small watercraft, which is adapted to supply a fuel in a fuel tank to an injector via a fuel supply pipe by means of a fuel pump. The fuel supply apparatus returns excess fuel from the injector to the fuel tank via a fuel return pipe and has a fuel cooling device in the portion of the fuel supply pipe which is between the fuel pump and the injector.
With such an apparatus, the fuel drawn from the fuel tank and about to enter the injectors is cooled by the fuel cooling device. This enables the fuel to be cooled and then supplied to the injectors efficiently as compared with a case where the return fuel is cooled. As a result, injection of the fuel is done properly by the injectors.
Preferably, the circulating fuel supply apparatus for the engine of the small watercraft has a heat exchanger that uses a cooling water as the fuel cooling device. This enables the fuel cooling device to be simplified, and the manufacturing costs to be reduced.
Preferably, the heat exchanger uses, as cooling water, an exchanger external cooling water taken in from the outside by a water jet propulsion unit of the watercraft, and the external cooling water which has been used to cool the fuel is discharged to the outside of the watercraft. Such enables maintenance of the cooling water to be done simply, the running costs to be reduced, and the fuel cooling effect to be increased as compared with a similar apparatus in which the internal cooling water is circulated in a closed circuit.